1. Field of the Invention
The present invention relates to cooking appliances, and particularly to a cooking appliance that detects the temperature of a foodstuff placed on a turntable using an infrared sensor.
2. Description of the Background Art
A microwave oven including an infrared sensor can be referred to as a first conventional example of a cooking appliance. In such a microwave oven, the foodstuff is placed on a rotating turntable. An infrared sensor senses the infrared radiation emitted from that foodstuff in the sense field thereof (the range where the infrared sensor can sense infrared radiation). The temperature of that foodstuff is detected according to the amount of sensed infrared radiation. Heating of the foodstuff is continued until the temperature of the foodstuff arrives at a predetermined consummation temperature of the foodstuff.
Arrangement of the foodstuff on the turntable varies corresponding to the number of foodstuff placed on the turntable in such a microwave oven. This means that the portion of the foodstuff within the sense field of the infrared sensor differs. If the portion of the foodstuff within the sense field of the infrared sensor differs, the detected temperature of the foodstuff corresponding to the sensed infrared radiation may change.
For example, consider the case where a bottle containing liquor, curved in shape and with height, is to be heated as the foodstuff.
When there is only one foodstuff such as one bottle, the arrangement of the bottle at the center of the turntable allows the portion of the bottle within the sense field of the infrared sensor to be always constant even when the turntable is rotated. Therefore, the temperature detected using an infrared sensor is identical when the temperature distribution of the bottle (foodstuff) is identical.
However, when there are a plurality of foodstuffs such as a plurality of bottles, the portion of each bottle that will be located within the sense field of the infrared sensor will vary according to the rotation of the turntable. More specifically, the section of the bottle within the sense field of the infrared sensor may be the neck portion of the bottle that exhibits rapid increase in temperature due to convection and the like or be the bottom portion of the bottle where the temperature increase is slow. There will be deviation in the detected temperature of the foodstuff.
When the number of the foodstuff increases in such a microwave oven, there is a case where the portion of the foodstuff of faster rise in temperature is located within the sense field of the infrared sensor than that of the infrared sensor for only one foodstuff due to the rotation of the turntable. There was a problem that the detected temperature of the foodstuff becomes ostensibly higher than the case where the number of foodstuff in the same state is only 1.
The operation of heating is stopped when the detected temperature of the foodstuff once arrives at the consummation temperature in the above-described microwave oven. Since there is an occasion where the detected temperature of the foodstuff when increased in number becomes higher momentarily than when only one in number, there was a problem that the actual consummated temperature becomes lower than the preset consummation temperature.
To solve such a problem, an approach can be considered of detecting the number of foodstuffs and applying correction according to the number of foodstuffs with respect to the detected temperature of foodstuff.
A microwave oven having the heating time determined according to a set cooking menu, absent of detection by an infrared sensor, can be referred to as a second conventional example of a cooking appliance. Such a microwave oven had the disadvantage that the foodstuff, when increased in number, is less easily heated to result in change in the actual consummated temperature of the foodstuff. In other words, the number of foodstuffs must be detected in that type of microwave oven, likewise the first conventional example.
A microwave oven including a weight sensor to detect the number of foodstuffs can be referred to as the third conventional example of a cooking appliance. The weight of the container of the food item will be included in the weight of the foodstuff when a weight sensor is employed. There is a case where the number of the foodstuffs cannot be detected properly depending upon the container that is used.
In the microwave oven of the first conventional example, the portion of the foodstuff located within the sense field of the infrared sensor will differ depending upon whether it is placed at the center or edge of the turntable even when the number of foodstuffs is identical.
For example, the portion of the foodstuff and the altitude (position in the height direction) of the foodstuff located within the sense field of the infrared sensor differ depending upon whether the foodstuff is located close to or remote from the infrared sensor. Because of heat convection, the portion of the foodstuff of higher altitude is generally higher in temperature than the portion of the foodstuff of lower altitude. Also, the detected temperature of a foodstuff becomes higher for a foodstuff having a larger proportion thereof in the sense field due to its close location to the infrared sensor than a foodstuff having a smaller proportion within the sense field such as in the case of being located remote from the infrared sensor, even when under the same condition.
In other words, the above first conventional example may have a different detected temperature of the foodstuff depending upon the location on the turntable, even when under the same condition. Thus, there was a problem that the actual consummated temperature differs depending upon the location of the foodstuff on the turntable even when the preset consummation temperature of the foodstuff is identical.